UV curable coating compositions, abrasion resistant UV stabilized thermoplastic composites and method

ABSTRACT

Organophosphorus compounds capable of being activated with light at from 360 nm to about 410 nm, such as, an acylphosphine oxide, have been found useful as photoinitiators for effecting the cure of various UV curable coating compositions, such as a UV curable organic material in the presence of up to 20% by weight of a UV absorber. UV stabilized thermoplastic composites of films, sheets, or laminates having thickness of up to an inch or more with improved optical clarity also are provided.

This application is a continuation of application Ser. No. 07/489,145,filed Mar. 5, 1990 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to UV curable organic coatingcompositions, such as a UV curable organic material, a UV curableorganosilicon material, or a mixture thereof, in combination with aphotoinitiator in the form of an acylphosphorus compound capable ofbeing activated by light with a wavelength in the range of from about360 nm to about 410 nm and selected from the class consisting ofacylphosphine oxides, acyl phosphonates and acylphosphine sulphides, andup to about 20% by weight of the UV curable coating composition of a UVscreen. More particularly, the present invention relates to certainweather and abrasion resistant thermoplastic composites havingthicknesses of up to 1 inch, or more which can exhibit improved opticalclarity, and which comprise a thermoplastic substrate such as apolycarbonate film or sheet, and a cured polyacrylic orpolyacrylic-urethane coating.

Prior to the present invention, as shown by Clark, U.S. Pat. No.4,027,073, heat curable silicone hard coat formulations were availablewhich could be applied to a variety of thermoplastic substrates, such asa polycarbonate or polyester in the form of film or sheet. Althoughuseful results can be obtained by employing such heat curable coatingcompositions, an organic solvent is used which is environmentallyunattractive. In addition, long process times are required to make asatisfactory abrasion and weather resistant composite of a thermoplasticsubstrate and hard coat.

Abrasion resistant thermoplastic composites having improved opticalproperties also can be made by effecting the cure of a solventlessradiation curable coating composition which has been applied onto thesurface of a polymeric sheet or film. The cure of the applied coatingmaterial can be effected while it is in contact with a smooth surface(cold casting) by directing radiant energy through the substrateopposite the surface being coated. The "cold-casting technique" isfurther illustrated in the copending application of Crouch, Ser. No.812,619, filed Dec. 23, 1985. Although improved surface characteristicscan be achieved with the radiation curable coating compositions ofCrouch, the resulting abrasion resistant thermoplastic film can sufferfrom reduced weathering resistance unless a latent UV screen is usedwhich does not interfere with the cure of the UV curable coatingcomposition while it is on the substrate.

Suitable latent UV screens, are for example, sulfonate esters ofhydroxybenzotriazoles, as shown by Olson, U.S. Pat. 4,344,830, which isincorporated herein by reference. These latent UV screens can impartimproved weathering resistance over extended periods of time, whilesimultaneously allowing the cure of the radiation curable coating.Although composites of thermoplastic films having thicknesses up toabout 30 mils, or sheets having thicknesses of up to about an inch canbe made by treating the films or sheets with a UV curable coatingcomposition and thereafter effecting the cure of the coating compositionin the presence of a latent UV screen, experience has shown that latentUV screens often have limited solubility in the coating composition. Inaddition, these latent UV screens frequently separate from the curedresin after an extended weathering period resulting in a marred,unattractive surface.

It would be desirable therefore to provide solventless UV curablecoating compositions which are capable imparting improved weathering andabrasion resistance to a variety of thermoplastic substrates in arelatively short period of time when applied and cured thereon. It alsowould be desirable to provide composites of thermoplastic films orsheets having a UV cured abrasion resistant polyacrylic orpolyacrylic-urethane coating having a thickness of about 4 to 15 micronswhich can contain an effective amount of a conventional instead of alatent UV absorber, and possess superior optical characteristics.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that the employment of aphotoinitiator, such as an acylphosphorus compound, for example, anacylphosphine oxide, having a spectral response in the range of betweenabout 360 nm to about 410 nm, can be used to initiate thephotopolymerization of various UV curable organic or UV curableorganosilicon materials in the presence of up to 20% by weight of aconventional UV absorber, such as a 2-hydroxybenzophenone, or a2-hydroxyphenyl-2H-benzotriazole.

STATEMENT OF THE INVENTION

There is provided by the present invention, a UV curable coatingcomposition comprising a UV curable organic material, a UV curableorganosilicon material, or a mixture thereof, an amount of anacylphosphorus compound which is effective for polymerizing theradiation curable organic coating composition upon exposure toradiation, and from about 0.5% to about 20% by weight of a UV screen,based on the total weight of the UV curable organic coating composition,where the acylphosphorus compound can be activated by light having awavelength in the range of from about 360 nm to about 410 mn and is amember selected from the class consisting of acylphosphine oxides, acylphosphonates and acylphosphine sulphides.

Some of the acylphosphorus compounds which can be used in the practiceof the invention are for example, 2,4,6-triorganobenzoyldiarylphosphineoxides, such as, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and2,4,6-triethylbenzoyldinaphthylphosphine oxide; 2,4,6-triorganobenzoyldiorganophosphonates, such as, 2,4,6-trimethylbenzoyl diethylphosphonateand 2,4,6-triethylbenzoyl diphenylphosphonate;2,4,6-triorganobenzoyldiarylphosphine sulfides, such as2,4,6-trimethylbenzoyldiphenylphosphine sulfide.

Included among the UV curable organic or organosilicon materials whichcan be employed in the practice of the present invention in combinationwith the acylphosphorus compounds include, for example, the hydrolysisproducts of silylacrylate and aqueous colloidal silica, and optionallyin further combination with a polyfunctional acrylate, as shown byOlson, et al, U.S. Pat. No. 4,455,205, or Chung, U.S. Pat. No.4,486,504, which are incorporated herein by reference. Additional UVcurable organic or organosilicon materials which can be used in thepractice of the present invention in combination with the acylphosphoruscompounds are UV curable materials as shown by Chung, U.S. Pat. No.4,478,876, Campbell, U.S. Pat. No. 4,477,529, and by Moore, et al, U.S.Pat. No. 4,198,465, which patents are incorporated herein by reference.

As used herinafter, the term UV absorber or UV screen, or UV stabilizer,as distinguished from latent UV absorber, or latent UV screen, includescompounds selected from 2-hydroxybenzophenones,2-hydroxyphenylbenzotriazoles and phenyl cyanoacrylates, which UVabsorbers have an absorbance value when exposed to light in the range offrom about 280 nm to about 360 nm. Some of the UV absorbers which can beutilized in the practice of the present invention in combination withthe acylphosphorus compounds are conventional UV screens, such as2-(2-hydroxy-5-t-octylphenyl)-benzotriazole,2-hydroxy-4-n-octoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone,ethyl 2-cyano-3,3diphenylacrylate and2-hydroxy-4-acryloxyethoxybenzophenone.

Suitable substrates which can be treated in accordance with the practiceof the present invention with the radiation curable organic coatingcomposition to impart improved abrasion resistance, as well as improvedweathering resistance are for example, thermoplastic films and sheets oforganic thermoplastic polymers, such as aromatic polycarbonates,aromatic polyesters, polymethylmethacrylate, polystyrene,polyetherimides, and other high performance thermoplastics which canbenefit from the treatment of the abrasion resistant coatingcompositions of the present invention. Depending upon the particularapplication, there can be used thermoplastic substrates in the form offilms having a thickness ranging from at least 0.5 to 249 mils andthermoplastic sheet having a thickness of up to 1 inch, and preferable0.25 to 0.5 inch.

As taught by Crouch, copending application Ser. No. 812,619,thermoplastic substrates with controlled surface characteristics can beobtained by applying the uncured radiation curable coating compositionto the film followed by expelling air from the coating. The coating isthen cured by directing radiant energy, such as ultraviolet light,through the film surface opposite the coated surface while it is incontact with a smooth or patterned substrate, such as highly polishedchrome or plastic.

In instances where an inflexible thermoplastic sheet is treated with theUV curable composition of the present invention to impart improvedsurface characteristics thereto, the thermoplastic sheet can be treatedinitially with uncured coating material using a curtain coater, or rollcoater followed by contacting the uncured coating material on thethermoplastic sheet surface with a flat sheet having a smooth orpolished surface, such as a rigid plastic or metallic sheet, andthereafter passing radiant energy through the opposite thermoplasticsheet surface to effect cure of the coating material. The flat sheethaving the polished surface can thereafter be separated from the curedcoated article.

In instances where shaped thermoplastic substrates are desired havingsurfaces with improved optical clarity, fabrication of a mold having ahighly finished inner surface is preferred. The coated thermoplasticpart can be contacted to the smooth mold cavity prior to exposure toradiant energy.

An alternative method for making thermoplastic sheet having a highlyfinished abrasion resistant and weather resistant coating, is tolaminate a treated thermoplastic film which has been cold casted with aUV curable organic coating material containing a UV absorber to athermoplastic sheet. Lamination of the treated film to the rigidthermoplastic can be effected by using a UV curable material as anadhesive.

In addition to the aforementioned ingredients shown in the Statement ofthe Invention, the UV curable coating compositions of the presentinvention also can contain other ingredients, such as anti-oxidants, andhindered amine light stabilizers. An effective amount of theacylphosphorus compound is from about 0.3 part to about 10 parts byweight of the acylphosphorus compound, per 100 parts by weight of the UVcurable coating material.

As indicated, cure of the organic coating material is preferablyeffected by using UV irradiation which can have a wavelength of from 360nm to 410 nm. The lamp systems used to generate such radiation canconsist of ultraviolet lamps such as from 1 to 50 discharge lamps, forexample, xenon, metallic halide, metallic arc, such as a low, medium orhigh pressure mercury vapor discharge lamp, etc. having an operatingpressure of from a few millitorr to about 10 atmospheres, etc., can beemployed. The lamps can include envelopes capable of transmitting lightof a wavelength of from about 184 nm to 800 nm, and preferably 240 nm to450 nm. The lamp envelope can consist of quartz, such as Spectrocil orPyrex, etc. Typical lamps which can be employed for providingultraviolet radiation are for example, medium pressure arcs, such as theGE H3T7 arc, etc. The cures may be carried out with a combination ofvarious lamps, some or all of which can operate in an inert atmosphere.In operating the lamp to achieve a desirable level of flux intensityrequired for effecting cures of the solventless coating composition in apolution free manner, the lamps can be ballasted to provide a higherwatts per inch input than that normally rated by the manufacturer. Forexample, the GE H3T7 lamp normally operated at 130 watts per inch, canbe operated at up to 300 watts per inch input over a satisfactoryoperating life.

In order that those skilled in the art will be better able to practicethe present invention, the following examples are given by way ofillustration and not by way of limitation. All parts are by weight.

EXAMPLE 1

A radiation curable organic coating composition is prepared consistingof 57 parts of an aliphatic acrylated urethane (Echo resin ALU-2 of theEcho Resin and Laboratory Company, Varsailles, Missouri), 17 parts of amonofunctional acrylic carbonate monomer Acticryl 959 of SNPE Inc.Princeton, NJ or Bergerac Cedex, France, 7 parts of2-hydroxy-4-n-octoxybenzophenone (Cyasorb 531 of American Cyanamid,Wayne, New Jersey) and 2 parts 2,4,6 trimethylbenzoyldiphenylphosphineoxide, (Lucirin TPO of BASF Aktiengesellschaft, Ludwigschafen, WestGermany or Cherry Hill, New Jersey).

The radiation curable coating composition is applied onto a 15 mil Lexanpolycarbonate film in accordance with the cold cast procedure shown byCrouch, European patent application no. 0,228,671 abandoned publishedJul. 15, 1987, or Ser. No. 812,619 filed Dec. 23, 1985. The curablecoating composition is applied to the film followed by expulsion of airfrom the coating by adjusting the pressure of the nip resulting fromcontact between the coated film and the smooth drum surface. Cure iseffected using two Linde medium pressure mercury lamps operating at atotal dose of 6.2 Joules/cm². The line speed is 20 ft/min and curetemperature is 105° F. There is obtained a composite of a polycarbonatefilm having a tackfree coating which exhibits excellent optical clarity,and superior weathering resistance.

EXAMPLE 2

The radiation curable composition of Example 1 is applied to a 4"×4.5"0.25 inch thick Lexan polycarbonate panel using wire-wound draw-downbar. The treated panel is then UV cured in a model 1202AN UV processor,manufactured by the Pittsburgh Plate Glass Company, at a belt speed of20 ft/min, under a nitrogen flow of 20 scfm, and at least 100 psi,resulting in a well-cured, tack-free coating.

As a result of the presence of Cyasorb-531, the resulting Lexanpolycarbonate composite has a cured coating of an aliphatic acrylatedurethane possessing excellent weathering characteristics.

EXAMPLE 3

A radiation curable composition was prepared by adding 70 parts ofmethacryloyloxypropyltrimethoxysilane to 468.3 parts Nalcoag 1034Ahaving 34% by weight of colloidal silica in water and a product of theNalco Company of Oak Brook, Ill. and 2250 parts isopropanol. There alsowas added, 0.2 part of methoxyhydroquinone as an inhibitor. The mixturewas refluxed for 1.5-2.0 hrs, and 195.3 parts of hexanediol diacrylatewas added. Volatiles were removed under 70 mm Hg of pressure There wasadded to 91 parts of the resulting coating composition, 7 parts2-(2-Hydroxy-5-t-octylphenyl)-benzotriazole, (Cyasorb 5411) a UV-lightabsorber of American Cyanamid and 2 parts of2,4,6,trimethylbenzoyldiphenylphosphine oxide (TMBPO).

The above coating composition was applied at 105° F., to a 15 mil Lexanpolycarbonate film at a line speed of 30 ft per minute in accordancewith the previously described cold-cast method of Example 1. Adhesiontesting of the resulting coating was done by scribing the coated areawith a Gitterschmitt prufgerat cross-hatch cutter, applying 3M 610 tapeto the cross-hatched area and rapidly pulling the tape from thecross-hatched area. Any coating removed constitutes failure. Abrasionresistance was determined by measuring the change in haze (%H) using aGardner XL 800series Haze Meter before and after 500 cycles on a model5150 Taber Abraser of Teledyne, North Tonawanda, New York, equipped withSC-10F wheels and 500 g weights. Accelerated weathering was done byplacing samples in a QUV device sold by the Q-panel Company ofCleveland, Ohio, set to consecutive cycles of fluorescent UV light usingB lamps for 8 hours at 70° C. and 4 hours of high humidity at 50° C.Outdoor accelerated weathering in Arizona using the Sun10Fresnel-reflecting concentrator, with night time wetting, according toASTM test D4141-C, was conducted by South Florida Test Service, Miami,Florida, a division of Atlas Electric Devices. The % Haze and YellowIndex (YI) was measured using a Gardner mode Haze meter model XL 800 andColorimeter, model XL 835.

In addition to the above UV curable coating composition, additionalcompositions were prepared containing the same coating composition butdifferent classes of UV light absorbers. The results obtained are shownin the Table below where TMBPO is trimethylbenzoylphenylphosphine oxideand Cyasorb-416 is 2-hydroxy-4-acryloxyethoxybenzophenone. The Tablebelow also shows a coating composition using 2 parts of a commercialphotoinitiator, Daracur 1664 of EM Merck, Hawthorne, New York, and 7parts of a latent UV screen in the form of a sulfonate ester of2-(2-hydroxy-5-t-octylphenyl)-benzotriazole.

    ______________________________________                                                      Taber Haze                                                                              OUV       %                                           Coating composition*                                                                        (500 cycles)                                                                            Hrs**     Haze YI***                                  ______________________________________                                        2   parts TMBPO   7.8       1390-1580                                                                             1.0  1.0                                  7   parts Cyasorb 5411                                                        0.5 parts TMBPO   9.1       1390-1580                                                                             1.6  1.8                                  12  parts Cyasorb 416                                                         2   parts Daracur 1664                                                                          7.4       500-880 3.1  7.4                                  7   parts Sulfonate ester                                                     ______________________________________                                         *Coating compositions all cured by coldcast at 30 ft/min and 105F             **Hrs before observable microcracking of the coating. Measurements made       about every 250 hrs.                                                          ***% Haze and YI measured after an accelerated aging test equivalent to 2     yrs in South Florida (398,620 Langleys).                                 

The above results show that the TMBPO composition at 0.5 part has asuperior QUV performance and % haze to the commercial Daracur 1664photoinitiator at 2 parts in combination with a latent UV screen.

EXAMPLE 4

A UV curable coating composition was prepared with 93.5 parts of thecoating composition described in Example 3,5 parts2-(2-hydroxy-5-t-octylphenyl)-benzotriazole (Cyasorb 5411 of AmericanCyanamid, Wayne, New Jersey). The coating composition was applied to0.25 inch thick Lexan polycarbonate sheet, stabilized with approximately0.3% Cyasorb 5411, by sandwiching the coating composition between thepolycarbonate plaque and a thin glass plate, thus excluding the oxygenfrom contact with the coating composition. The treated panel was then UVcured through the stabilized polycarbonate sheet in a model 1202AN UVprocessor, of the Pittsburgh Plate Glass Company, at a belt speed of 20ft/min under air atmosphere using two 300watt/linear inch lamps. Thethin glass plate was then removed. There was obtained a composite havinga hard tack free optically clear coating which was resistant toscratching using steel wool.

EXAMPLE 5

A UV curable adhesive composition is prepared from 70 parts of analiphatic urethane Abcure 2164 of American Biltrite, Trenton, NewJersey, 9.5 parts hexanediol dicarylate, 17.5 parts n-vinylpyrrolidone,and 3 parts 2,4,6 trimethylbenzoyldiphenylphosphine oxide. It is used tolaminate a 36 inch×0.015 inch/Lexan polycarbonate film, which had beentreated with the coating composition as described in Example 3, andthereafter cured in accordance with Example 1. The coated film islaminated to a 36 inch×0.25 inch Lexan polycarbonate sheet by initiallytreating the 0.25 inch polycarbonate sheet with the above UV curableadhesive, contacting the 0.015 inch film section onto to treated sheetsurface and there after effecting the cure of the adhesive in accordancewith the procedure of Example 4.

There is obtained a polycarbonate laminate having excellent opticalclarity and weatherability.

Although the above examples are directed to only a few of the very manyvariables which can be used in the practice of the present invention, itshould be understood that the present invention is directed to a muchbroader variety of UV curable organic coating compositions and tothermoplastic composites made by using such radiation curablecompositions as set forth in the description preceding these examples.

What is claimed is:
 1. A UV curable coating composition consisting essentially of by weight(A) 100 parts of a mixture of a UV curable polyfunctional acrylate, and a UV curable hydrolysis product of silylacrylate and arqueous colloidal silica, (B) 0.3 to 10 parts of an acylphosphine oxide which is effective for polymerizing the UV curable organic coating composition with light having a wavelength of from about 360 nm to about 410 nm and (C) a UV absorber, where the UV absorber is used in the UV curable coating composition in an amount which is sufficient to provide a weight ratio of acylphosphine oxide to UV absorber having a value of about 0.04 to about 0.3.
 2. A UV curable coating composition in accordance with claim 1, where the acylphosphineoxide is 2,4,6-trimethylbenzoyldiphenylphosphine oxide.
 3. A UV curable coating composition in accordance with claim 1, where the UV absorber is 2-(2-hydroxy-5-octylphenylbenzotriazole.
 4. A UV curable coating composition in accordance with claim 1, where the UV absorber is 2-hydroxy-4-n-octoxybenzophenone.
 5. A UV curable coating composition in accordance with claim 1 where the polyfunctional acrylate is hexanediol diacrylate. 